DESCRIPTION: (applicant's abstract) The first long-term objective of this research is to understand the catalytic mechanism of the terminal oxidase, cytochrome c oxidase. This is to be accomplished by synthesizing and characterizing functional models of the dioxygen binding activation site in cytochrome c oxidase. Newly developed methods will be used to prepare Fe porphyrins fitted with tridentate Cu complexes on the distal face of the porphyrin and imidazole axial ligands covalently attached to the proximal face. These models will be characterized by X-ray diffraction and a range of spectroscopic methods. Each model complex will be examined as a putative electrode catalyst for the 4-electron reduction of O2. The mechanism of these electrocatalytic reactions will be explored; each stage will be examined separately; intermediates will be characterized. It is hoped that the function of these catalysts will help us understand the enzymatic reaction, especially the role of CuB. A second objective is to understand the role which distal residues play in controlling the relative equilibrium binding of three naturally occurring gaseous ligands: O2, CO, and NO. This will be accomplished by studying new cavity porphyrin sandwiches and dendrite porphyrins. The role of distal steric effects and of H-bonding will be explored. The NO binding has relevance to many medical problems related to activation by the gaseous hormone, NO. Examples include vasodilation and neurotransmission.